Pulsed laser applications, such as materials processing, require a known amount of laser energy incident upon the material being processing. In most of these applications, process control is achieved by controlling the energy incident upon the surface of the material. Therefore, for such industrial applications, laser systems utilize all energy detector which measures the energy of each laser pulse. This energy information is communicated to the system user by the laser-based micro-controller, wherein the user can modify operating conditions to maintain constant laser energy or change the laser's energy to a new value.
Unlike lamps, which are discarded after use, gas discharge type lasers have to be maintained at specified intervals during use in a production environment, and the various subsystems must be refurbished due to contamination resulting from the various laser gasses reacting with the electrodes and chamber materials. This type of contamination, generally in the form of a metal fluoride dust in excimer laser systems, causes deterioration in the beam profile and bandwidth increases as a result of deposition and/or etching of the laser's windows. Erosion of the lasers electrodes during operation as a result of arcing and fluorine passivation in turn causes degradation of the laser's bandwidth, degradation of pulse-to-pulse energy stability, inconsistent burst mode behavior and degradation in beam profile. As the number of total pulses output by the laser increases during normal operation, sub-components such as the thyratron switch and the line narrowing modules likewise degrade in performance, resulting in less-than-expected energy output from the laser and an overall loss of process control. Typically, if the laser energy deviates too far from a user-specified range, the laser controller will terminate laser operation, thereby resulting in costly down-time for the user.
Industrial laser systems currently manufactured, have built in diagnostics to monitor system performance and help the user identify the cause of the laser's deteriorating performance. One such system is described in U.S. Pat. No. 5,377,215, assigned to the assignee of the present invention and specifically incorporated herein by reference as part of this disclosure. Diagnostics, such as those described in the '215 patent, utilize sensors placed in various critical locations within the laser; wherein the laser's micro controller continually monitors the inputs from these sensors and updates the memory locations used to store the individual inputs. These types of diagnostics provide a snapshot of the laser's status at the instant the sensory information is downloaded from memory, and are therefore limited to providing notice to the user once a problem occurs; they are not capable, however, of providing predictive information, based upon sub-component deterioration and sub-component end-of-life information, as to when a probable failure could occur.